Exhaust silencer



Sept. 9, 1941. J. G. BLANCHARD EXHAUST S ILENCER Filed Nov. 14, 1939 4 Sheets-Sheet l Inventor A fame P 1941- J. G. BLANCHARD 2,255,579

EXHAUST S ILENCER Filed Nov. 14, 1939 4 Sheets-Sheet 2 JZJg' /Z (g g Inventor A ltorney Sept. 9, 1941.

J. G. BLANCHARD EXHAUST S ILENCER Filed Nov. 14, 1939 4 Sheets-Sheet 3 (9 24 o o 0 2s A ltorney Sept. 1941- J. G. BLANCHARD 2,255,579

EXHAUST SILENCER Filed Nov. 14, 1939 4 Sheets-Sheet 4 Inveninr Patented "Sept. 9, 1941 2,2555 nxnavs'r smmcsn Joseph George Blanchard, London, England, as-

signor of one-half to Cecil Gordon Vokes, London,

Application November 14, 1939, Serial No.

In Great Britain November 14, 1938 11 Claim.

This invention relates to silencing apparatus for use with the exhaust gases of internal combustion engines and is more especially, though not exclusively, intended for application to silencing systems for use with engines installed in aircraft.

Silencing apparatus in accordance with the invention comprises a plurality of silencing units mounted within a common casing, each having a separate inlet for gases and a path by which gases may escape into the interior of the common casing, the latter beingprovided with a plurality of outlets by way of which gases may escape from the units and from the interior of the common casing.

In a preferred form of apparatus, the silencer units have casings which are perforated to provide paths for the escape of gases into the common casing and each unit is spaced from an outlet orifice in the wall of the common casing which serves for the more or less direct escape of gases from the unit and also, in parallel with the other outlet orifices, for the escape of gases which have passed into the interior of the common casing by way of the perforations in the walls of the units.

The efllciency of the systems may be increased by the provision of rearwardly directed orifices past which the slip stream flows to exercise an entraining effect upon the gases: the orifices may be formed in a cover member which fits over part of the common casing and also acts as a flame trap or they may be formed in the wall of the common casing itself.

The invention is illustrated by the particular examples of silencing systems which will now be described with reference to the accompanying drawings, in which:

Fig. 1 represents an elevation, partly in section, of a silencing system for an in-line engine,

Fig. 2 represents an exhaust scavenger and flame trap device for use in the system illustrated by Fig. 1,

Fig. 3 represents a section, on the line III-III of Fig. 1, through the silencing system, with the device of Fig. 2 in position;

Fig. 4 represents a section on the line IV-IV of Fig. 5, through a modified system, whilst Fig. 5 represents a section on the line V V of Fig. 4.

Fig. 6 represents a front view of a silencing system for a radial cylinder engine, and

Fig. 7 represents a section on the line VIIVII of Fig. 6.

The silencing system illustrated by Figs. 1 and 2, which is intended for use with an engine having four cylinders in line, or a bank of four cylinders in line, comprises an elongated outer casing I (which will be referred to hereinafter as the common, casing) in which four silencer units 2 are arranged with their longitudinal axes at right angles to the longitudinal axis of the common casing I.

Each unit, which is of the type described in my British specification No. 448,878, is provided with an inlet pipe 3 by which it receives gases from one of the engine cylinders and the units are spaced apart in the same way as the engine cylinders so that the inlet pipe of each unit may be a substantially straight, preferably short pipe. The common casing I is provided with four outlet orifices each coaxial with one of the units and its inlet pipe, and each unit is spaced from the corresponding outlet orifice, so that the interior of the common casing around the units communicates with the atmosphere by way of four parallel paths.

Each of the silencer units 2, which are made of heat-resisting material, has an outer perforated casing 5, one end of which is welded to the inner wall of the common casing I and to a curved annular plate 6 which conforms to the inner wall of the common casing, a cupped end plate 1 closing the other end of the perforated casing 5 and carrying a coaxial outlet tube 8, and a tubular member 9 of Venturi form. The tubular member 9 is secured by lugs III to the perforated casing at one end, where it surrounds with considerable clearance the inner end of the outlet tube 8, and at the other end surrounds with less clearance a short tube II to which it is secured by lugs I2: the short tube II forms a continua-v tion of the inlet pipe 3 and is welded to another short tube I3 which receives the end of the pipe I and is itself welded to the common casing.

The units are supported at the outlet end by bolts I4 which pass through the common casing I and are screwed into nuts I 5 welded to the cupped end plates I. Gases entering a unit by way of its inlet pipe and which do not pass directly to the atmosphere by way of the corresponding outlet tube 8 and orifice 4, may expand and pass into the interior of the common casing by way of the perforations in the casing 5. Since each unit receives gases from one cylinder only of the engine and the cylinders fire at different times, the gases escaping from a unit by way of the perforations inits casing are able to use for expansion the whole of the interior of the common casing, whence they may easilyescape to atmosphere by way of the parallel paths provided by the four outlet orifices.

It is preferred so to arrange matters that the total area of the perforations in the casing of a unit and the cross sectional areas of the corresponding inlet pipe 3 and outlet orifice I are all approximately equal to each other.

The high pressure gases which pass out directly from the interior of a unit to the atmosphere by way of the outlet tube 8 and corresponding outlet orifice 4 exercise an injector or entrammg effect upon the atmosphere within the interior of the common casing i: there is thus an almost continuous scavenging effect upon the interior of the common casing, which assists the expansion of the gases.

The scavenging eifect is increased by the use of rearwardly-opening hood members l6 outside the outlet orifices l and is still further augmented by the provision of an outer cover member which also acts as a flame trap.

The cover member ll, which is welded to the common casing I and encloses the hood members l6, has a number of rearwardly-facing apertures l8 formed by slotting the wall of the member and pressing inwardly substantially triangular portions iii. For strengthening purposes, the wall of the cover member I1 is outwardly swaged as at 20 immediately in front of each aperture N, the swaged portions extending between the remote extremities of the corresponding apertures, that is to say almost from edge to edge of the cover, as will be seen from Fig. 3.

The slip stream passing the apertures i8 exercises a strong scavenging effect upon the interior of the space between the cover H and the common casing l and thence upon the interior of the common casing,

In addition to its silencing properties, a system in accordance with the invention is found to offer advantages in connection with weight reduction, tests having shown that the weight of the, whole system can be approximately equal to thajtpf the manifold employed in a comparable system,to collect exhaust gases from several cylinde'rs and convey them to common silencing means. v

By virtue of its relatively low weight, the silencing system illustrated may not need to be secured to the aircraft otherwise than through the pipes 3 and the associated engine. If necessary, however, lugs 2| or other fixing means may be provided.

The gaseous atmosphere within the common casing l and outside the units 2 being, generally, cooler and less likely to contain flame than the gases passing directly through the units from the engine cylinders to the outlet orifices 4, is well suited for use in connection with the heating of the carburettor of the associated engine. For thizzpurpose, a connecting member is provided a In addition to the advantages mentioned above, a system as just described has, over previously proposed silencing systems, advantages in connection with the distribution of heat; in systems employing exhaust-collector manifolds, the manifold is subjected to the heat of the gases exhausted from all the cylinders with which the system is directly associated, and the same applies to common silencing means to which the gases from a number of cylinders are directed by a manifold or by separate pipes. In a system in accordance with the invention, each unit is subjected directly only to the heat of the gases escaping from the associated cylinder (or cylinders, if, by way of modification, more than one cylinder is connected to each unit) and is permitted to tend to cool during the intervals between the firing of the associated cylinder (or cylinders), since the major portion of the heat applied to each unit passes directly out to the atmosphere, by way of the associated outlet pipe, without aifecting to any great extent the other units or the wall of the common casing.

Moreover, the risk of fire occurring owing to highly inflammable fuel coming into contact with highly heated metal, for example in the case of an accident, is less than in normal systems: the portions of the units which come into direct contact with the hottest gases, namely the cupped end plates, are doubly enclosed by the wall of the common casing and the cover ll. The use of the hood members; I6 prevents flame and very hot gases coming into contact with the cover H so that highly heated portions of the outermost wall of the system are avoided.

The shape of the common casing of a system in accordance with the invention can be so chosen as to render it suitable for its location; thus, it can be suited to the available space when situated within the surface skin of an aircraft fuselage or engine nacelle or it can be of streamline form if,

as in the case of the system illustrated by Figs. 1 to 3, it is to be situated wholly or partly in the air-stream. The shape illustrated by Figs. 1 and 3, though not actually streamline, is found to be suitable for certain cases.

In the case of systems for use in connection with radial-cylinder aero engines, annular or part-annular common casings can be used. Such annular, or part-annular, casings will preferably be installed within the cowling rings of the engines behind the cylinders and be of streamline or other appropriate cross-section so as to interfere as little as possible with the flow of air which has passed over the cylinders.

In the modified arrangement illustrated by Figs. 4 and 5, the cylindrical perforated casings 5 are arranged with their axes parallel to the axis of the common casing I, to which they are secured by welding along the line 23. The ends 'of the casings 5 are closed by domed, perforated end plates 24 and tubular members 25, which take the place of the Venturi members 9 of the form previously described, are secured direct to the inlet pipe 3. The dished end plates 1 are welded to the perforated casings 5 as at 26 and are also supported by pairs of lugs 21. The outlet pipes 28 are formed with rearwardly-facing outlet orifices 29.

The common casing I may be provided with outlet orifices, as at 30, and a scavenger and flame trap cover similar to that illustrated at I! in Figs. 2 and 3 can be used or, alternatively, the common casing I may itself be provided with rearwardly-facing apertures, similar to the apertures l8 in the cover I! of Figs. 2 and 3, as indicated at 3| by dotted lines in Fig. 5. In either case, rearwardly-facing apertures can usefully be provided further forward than in the case of the cover ll, which receives gases solely by way of the rearwardly-directed hoods I6.

Advantages of this modified form of silencer are simplification, avoidance of the use of the bolts I of Fig. 3 and protection against fire risk, smce it will be observed that the cupped end plates 1 are trebly enclosed-by the perforated walls 5, the wall of the common casing and the cover, assuming that the latter is used. The use of outlet pipes 28 for the units with rearwardlydirected outlet orifices 28 prevents the very hot gases being directed upon a relatively small area of the wall of the common casing. The use of units having their axes parallel to the axis of the common casing also facilitates the fitting of them into casings of certain shapes or relative sizes. Thus, for example, an arrangement such as that illustrated by Figs. 4 and is particularly applicable to the case of a silencer for use with a radial engine having a common casing which is not circular in cross-section, as in the arrangements illustrated by Figs. 1 to 5, but is of substantially stream-lined cross-section.

The arrangement mentioned above in connection with Figs. 4 and 5 whereby no cover member such as I! is employed but rearwardly-facing outlet apertures 3! are provided in the wall of the common casing itself will probably be that most suitable for silencers for use with radial engines and r example of a typical system for a 14- cylinder radial engine is illustrated by Figs. 6 and 7.

In this system, the common casing i is made in four tubular portions, each of substantiallystream-lined shape in cross-section as shown by Fig. 7; the ends of the casing portions are flared outwardly to enable them to be secured together by means of split collars 40 having peripheral swages 4| in which the flared ends of the casing portions are received. The split in one of the collars appears at 42' in Fig. 6 and the collars are tightened up by means of bolts or the like at the rear of the casing, as indicated roughly in dotted lines at 43 in the case of the same collar.

The units, which are similar to those described above with reference to Figs. 4 and 5, are secured within the common casing by means of brackets 44 and receive gases from the respective cylinders by way of pipes 3.

Slots are formed in the peripheral wall of the casing between the collars 4| by cutting the tubular portions, as at 46 and 41 in Fig. 'l, and arranging plates 48, 49 and 50 in overlapping relation, also as shown in Fig. 7; a larger or smaller number of slots could be provided if desired.

The rear edges of the plates 48, 49 and SI! and also of the casing wall at 46 are swaged, as at 5!, for strengthening purposes and spacing means (indicated diagrammatically at 60) are provided between the various plates 48, 49 and 50 and the portions of the casing wall which they overlap: such spacing means may, for example, take the form of swages in directions at rightangles to those at Si or short tubular members may be placed between the surfaces to be spaced and be held in position by bolts or rivets.

The outer ends of the outlet pipes 28 are turned so that their outlet orifices face in the circumferential direction, whereby the hot gases are prevented from impinging directly upon the wall of the common casing. The outlet orifices may all face the same way, or those of the outlet pipes of adjacent units may face each other if desired.

Instead of providing a casing common to the units associated with each of the fourteen cylinders of the engine, the system might comprise two or more sections, for example four sections, each tubular portion of the casing being closed at the ends.

From Fig. 7 it will be seen that a substantial free space is provided behind the units, owing to the cross-sectional shape of the outer casing:

some of this space may be utilized for a useful purpose, for example for the provision of cabinheating arrangements. Thus, there is indicated in Fig. 6 an air-heating device 52 having an airinlet 53 and outlets 54 or a flash boiler might be situated in the space to heat water for a steamheating system.

Units of a kind other than specifically referred to above can be used as part of apparatus in accordance with the invention. Thus, for example, other forms of unit providing a straightthrough path for the gases could be employed or units as described in my British specifications Nos. 366,257 and 426,769.

The above somewhat specific descriptions of apparatus in accordance with the invention have been given by way of example and it is to be understood that various modifications may be made without departing from the invention.

I claim:

1. Silencing apparatus for exhaust gases of an internal combustion engine, comprising a common casing, a plurality of silencing units mounted therein, means defining a passage connecting each unit to a difl'erent cylinder of the engine, each unit providing an escape path for expansion of a part of the gases into the common casing and a main path for relatively high pressure gas and the common casing having a plurality of outlets for the escape of the relatively high pressure gas therefrom to exert under the influence of air passing said outlets an intraining effect upon that part of the gases expanded into the common casing.

2. Silencing apparatus for exhaust gases of an internal combustion engine, comprising a common casing, a plurality of silencing units mounted therein, means deflning a passage connecting each unit to a different set of cylinders of the engine, each unit comprising means defining an escape path for expansion of a part of the gases into the common casing and means defining a main path for relatively high pressure gas and the common casing having a plurality of outlets for the escape of the relatively high pressure gas therefrom to cause the relatively high pressure gas to exert under the influence of air passing said outlets an intraining effect upon that part of the gases expanded into the common casing.

3. Silencing apparatus for exhaust gases of an internal combustion engine, comprising a common casing, a plurality of silencing units mounted therein, means defining inlet passages for the respective units from difierent cylinders of the engine, the units each having an outlet defining with said inlet passage a substantially straight through path in parallel with the others and being further formed with lateral outlet passages defining a second and alternative path in parallel for the gases to escape and expand into the common casing and the common casing having a plurality of outlets for the escape of gas therefrom.

4. Silencing apparatus as claimed in claim 3, in which the units define substantially straight through paths to outlets in the wall of the common casing which outlets also serve in parallel for the escape of gases which have reached the interior of the common casing by way of the alternative paths.

5. Silencing apparatus for exhaust gases of an internal combustion engine, comprising a common casing, a plurality of silencing units mounted therein, means defining inlet passages connecting the respective units to different cylinders of the engine, each unit being constructed to provide an outlet communicating with the inlet passage to define a substantially straight through path and further formed with lateral passages to provide a second and alternative path for the gases to escape into the common casing and the common casing having a plurality of outlets for the escape of gas therefrom, and rearward defleeting means in the path of gases escaping from the common chamber.

6. Silencing apparatus for exhaust gases of an internal combustion engine, comprising a common casing, a plurality of silencing units mounted therein, means defining inlet passages connecting the respective units to different cylinders of the engine, each unit being constructed to provide an outlet communicating with the inlet passage to define a substantially straight through path and further formed with lateral passages to provide a second and alternative path for the gases to expand and escape into the common casing and the common casing having a plurality of outlets for the escape of gas therefrom, together with rearward deflecting means in the path of gases escaping from the respective units,

the through paths leading to the said rearward deflecting means.

7. The combination with the apparatus claimed in claim 3 of a cover member enclosing part of the common casing and provided with rearwardly directed openings.

8. The combination with the apparatus claimed in claim 3 of a cover member enclosing part of the common casing and provided with rearwardly directed openings and deflecting means within the cover member in the path of gases emerging from the straight through paths.

9. Apparatus as in claim 3 in which the units include substantially cylindrical outer casings the axes of which are transverse to the longitudinal axis of the common casing.

10. Apparatus as in claim 3 in which the units include substantially cylindrical outer casings the axes of which are parallel to the longitudinal-- axis of the common casing.

11. Apparatus as in claim 4 in which the units are secured within the common casing by welding along the lines of contact between the wall of the common casing and the substantially cylindrical outer casings of the units.

JOSEPH GEORGE BLANCHARD. 

